Hot water treatment in combination with calcium ascorbate dips increases bioactive compounds and helps to maintain fresh-cut apple quality

Abstract

Fresh-cut ‘Braeburn’ apple slices were dipped into cold water (4°C for 2min) or hot water (HWT, 48°C or 55°C for 2min) followed by dips into 0 or 6% w/v aqueous calcium ascorbate (CaAsc, 2min, 0°C) and stored in air up to 28 d at 4°C. Microbial counts, changes in browning and sensory acceptance were determined to indicate changes in quality. Changes in antioxidant levels were measured using free radical scavenging activity (DPPH), reducing activity (FRAP), ascorbic acid content (AA) and polyphenolic content (by HPLC). CaAsc dips had a strong impact reducing the browning through increasing the flesh luminosity and hue angle. 6% CaAsc in fresh-cut apples extended the overall acceptability from less than 7 d to 14 d. Immediately after CaAsc treatment, AA content was 5 fold higher (0.25–1.25gkg−1) than those not dipped into CaAsc. However, the combination of HWT treatments and CaAsc dips led to seven fold increased levels of AA inside the apple tissue (0.25–1.85gkg−1) and consequently increased the antioxidant activity. HWT did not increase the AA content when not combined with CaAsc dips. The HWT CaAsc dip extended the overall acceptability to 21 d compared to 14 d for samples not heated but dipped into CaAsc. Shelf life was ultimately limited by sensory quality. At day 28, total plate counts were reduced from 5.3logcfu/g (untreated slices) to 4.6logcfu/g in the 6% CaAsc dips and further to 3.9logcfu/g with the combination of HWT and CaAsc dip. Changes in the content of phenolic compounds with time, HWT and CaAsc dip were generally not significant except for slightly increased quercetin and phloridzin levels and decreased p-coumaric and procyanidins over time. The combination of HWT at 48°C for 2min followed by 6% CaAsc dip would be best for preserving the eating quality of apple slices.